One known apparatus for depositing films, particularly dielectric films, on workpieces, such as dielectric substrates, semiconductor wafers or metal substrates includes a vacuum plasma processor enclosure wherein a plasma gas supplied to a plasma chamber of the enclosure is excited to a plasma by a continuous, i.e. non-pulsed, microwave field. Ions in the resulting plasma chemically react with ions and other particles of at least one other element introduced into a reaction chamber to form deposited layers on the workpiece. The microwave field interacts with a DC magnetic field having lines of flux generally aligned and coaxial with a longitudinal axis of the microwave field. The frequency of the microwave field and intensity of the DC magnetic field cause an electron cyclotron resonance phenomenon in the reaction chamber. The workpiece is usually mounted on a holder; if the workpiece is non-metallic the holder is typically an electrostatic chuck including an electrode usually supplied with DC chucking voltage and an r.f. bias having a frequency such as 4.0 or 13.56 MHZ.
The microwave field interacts with electrons spiraling in the DC magnetic field to produce a high-density plasma when the vacuum chamber is maintained at a pressure of less than about 10 milliTorr. The electron cyclotron resonance arrangement increases ion production at these low gas pressures by efficiently coupling microwave energy to the plasma gas. At electron resonance, as established by the frequency of the microwave source and the DC magnetic field intensity, electrons in the plasma orbit the DC magnetic field lines at the same frequency as the microwave field. The electrons continuously gain energy from the microwave field and are accelerated with a circular motion about the microwave field axis, which is coincident with an axis of a source of the DC magnetic field, such as a solenoid coil. The DC magnetic field inhibits plasma electrons from losing energy to walls of the processor chamber, to increase the probability of ionization of elements in the plasma.
In one prior art arrangement, the DC magnetic field is 875 Gauss and the microwave field has a frequency of 2.45 gigahertz, derived by a magnetron and supplied to a first end of the plasma chamber via a matching network, a wave guide and a window. Typically, the plasma gas is a mixture of oxygen and an inert gas, such as argon. At a second end of the plasma chamber, opposite the first end thereof, electrons and ions escape from the plasma chamber into the reaction chamber. The electrons escape from the plasma chamber into the reaction chamber before the ions.
The electrons and ions pass through the reaction chamber. Exemplary gases supplied to the reaction chamber are a silane, such as SiH.sub.4, or a silane mixed with phosphine (PH.sub.3), tetrafluorosilane (SiF.sub.4) or nitrogen (N.sub.2). The chemical reaction takes place on the workpiece primarily between ions, typically O.sub.2.sup.-, escaping from the plasma chamber and molecules in, as well as ions dissociated from, the gases flowing into the reaction chamber, e.g. Si.sup.+, SiH.sup.+, SiH.sub.2, and SiH.sub.3.
Downstream of the reaction chamber, electrons and positive ions in the plasma are incident on the substrate. The silicon introduced into the reaction chamber and the oxygen ions dissociated from the plasma source gas combine on the workpiece, i.e., substrate, to form silicon dioxide layers which sometimes are doped with phosphorous, fluorine, or nitrogen, depending on the gases introduced into the reaction chamber.
There is a measurable nonuniform charge build up on dielectric layers being formed by the CVD process in gaps with relatively high height to width aspect ratios of at least 1:1. This charge build up is due to a disparity between the trajectories of the ions and electrons. This difference in trajectories is due to the large disparity in mass between ions and electrons, when exposed to an applied radio frequency electromagnetic field. The electrons are mobile enough to follow the applied r.f. field. The ions are not. This results in the dielectric layers being CVD formed acquiring charge separation, which then creates a net negative DC bias (also called applied bias) on the dielectric layer being formed. The net negative DC bias is with respect to the plasma, which usually has a voltage close to ground. The positive ions in the plasma see this negative bias and are accelerated to the surface of the dielectric layer being formed. The positive ion trajectories are very directional normal to the exposed layer surface because of this bias. As a result, positive ions accumulate on the bottom of a topographical structure, such as a trench or high aspect ratio dielectric layer. The electrons, on the other hand, being less directional, tend to collect at the tops of the topographical structure.
This separation in charge between the electrons at the top of the layer and the positive ions at the bottom of the layer can cause a destructive Fowler-Nordheim current to flow through the layer, its underlying active semiconductor device structure, and the substrate. The circuit is completed by current flowing back up to the plasma at some other location on the workpiece. This current flow through an active semiconductor device underlying the dielectric layer being found causes degradation of a gate oxide in a metal oxide semiconductor (MOS) device of the underlying structure.
It is, accordingly, an object of the present invention to provide a new and improved method of and apparatus for chemically vapor depositing materials in a vacuum plasma processor responsive to a plasma established by an electron cyclotron resonance mechanism.
Another object of the invention is to provide a new and improved method of and apparatus for electron cyclotron resonance chemical vapor depositing layers on a workpiece to provide a dielectric film or layer formed in such a manner as to substantially obviate the tendency for charge separation to occur in the formed film or layer between separated positive ions and electrons in the layer.
A further object of the invention is to provide a new and improved chemical vapor deposition method of and apparatus for depositing dielectric materials in a vacuum plasma processor wherein the plasma of the processor is excited by an electron cyclotron resonance mechanism energized in such a manner as to reduce damage due to separation of positively charged ions and electrons on opposite portions of the formed dielectric film.
An additional object of the invention is to provide a new and improved ECR, CVD method of and apparatus for forming layers in a high aspect ratio gap on a workpiece, wherein the compound in the gap has high uniformity.